Manufacture of propellant powder



Patented Feb. 27, 1945 its at MANUFACTURE or raoratmn'r PUWDER Leon W.Babcock, Wilmington, Del, asslgnor to Hercules Powder Company,Wilmington, Deb, a corporation of Delaware No Drawing. Application April11, 1941, Serial No. 388,083

12 Claims.

of the single or double base type, it is necessary to force the materialby means of presses into blocks and through forming dies. The pressurewhich is necessary to force the colloid into the desired form is usuallysupplied by means of a hydraulic ram under a pressure of 2,500 to 3,800pounds per square inch. The smokeless powder during the pressingoperations has been known to ignite and burn and in some instances hasbeen known to explode. These combustions destroy the powder inpractically all cases, often damage the press and expose operators topossible injury.

The object of this invention is to provide a method of pressingcolloided smokeless powder which will prevent instances of ignition,fire or explosion.

A further object of this invention is to provide an improved method ofoperating the hydraulic presses used in the smokeless powder art.

A further object of this invention is to provide a safer method forforcing colloided smokeless powder through forming dies.

A still further object of thi invention is to provide a method ofpressing solvent-containing smokeless powder which will eliminateaccidental ignition of the solvent vapors.

Other and further objects will be apparent hereinafter.

The objects of this invention have been accomplished by operating thehydraulic presses, in which the colloided smokeless powder is pressed inan atmosphere that is sufllciently inert to prevent the ignition and/orcombustion of any vapOrs present, or of the smokeless powder within thepress and to thus prevent the possibility of the vapors and/or powderfrom reaching a condition conducive to explosion. In particular, thepowder is maintained in an atmosphere incapable of supporting combustionduring the pressing operations and especially during the forcing of thepowder through forming dies.

More specifically in accordance with this invention the possibility ofignition, combustion, or explosion of the material in the hydraulicpresses has been materially reduced or completely eliminated byregulating the composition of the gaseous medium within the press and/orwithin pockets in the powder. The gaseous medium within the press andwithin pockets or occluded in the powder is normally air and during thepressing operations will contain varying percentages of solvent vapors,such as for example, ether, acetone, alcohol or the like depending onconditions of temperature etc. Further, the air may contain varyingpercentages of any volatile compound which is contained within thesmokeless powder. In accordance with this invention, the

,gaseous medium surrounding, in contact with and occluded by the powderis rendered inert, that is, incapable of supporting combustion bydecreasing the percentage of oxygen therein. This decrease may beaccomplished by sweeping out the press with inert gases such asnitrogen, carbon dioxide, helium, and the like or with, inert gaseousmixtures, such as flue gas, exhaust gas, producer gas, and the like.Further, an oxygen deficiency may be accomplished by raising theconcentration of the inert gas in the press such as, for example, byplacing solid carbon dioxide in the press before the press is closed orby forcing inert gases into the press after it is closed. Decreasing thepercentage of oxygen present produces a gaseous medium which will notsupport combustion and thereby prevents ignition, combustion orexplosion within the press. The ignition or combustion which must beprevented is that of the solvent Vapors as their ignition causes theignition of the powder present, and once the powder is ignited, it willsupport its own combustion due to the available oxygen therein.

The colloided powder before blocking and pressing has been found tocontain occluded gas and pockets of gas and in accordance with thisinvention this gas may be rendered inert and incapable of supportingcombustion, since it is likewise compressed during operation and mayignite, burn, or explode during the pressing. Rendering non-explosivethe gas which is in pockets or occluded within the powder may beaccomplished by mixing the powder in an inert atmosphere or by treatingthe mixed powder with an inert atmosphere so that any occluded gas orpockets of gas formed in subsequent operations will be incapable ofundergoing ignition.

The method in accordance with this invention may be employed in any stepof smokeless powder manufacture where it is necessary to press thematerial such as by means of a hydraulic press. Thus, after the powderingredients have been mixed especially with single base powders it iscustomary to force the lumpy material through what is known as amacaroni press. This press contains a perforated plate instead ofspecialized forming dies and the forcing of the smokeless powder throughthis plate insures proper mixing of the colloid. The method ofpreventing ignition, combustion or explosion by operating in an inertgaseous medium is applicable to this macaroni press. After the macaronioperation, the powder is blocked, that is, formed into a cylinder beforeit is put in the forming press. The blocking press may be operated underinert gaseous conditions. Further, with double base powder, the macaronipress may be used, but normally the double base powders after mixing arenot put through the macaroni press but are immediately formed intoblocks of powder suitable for insertion into final forming. presses. Theforming of the double base powder into blocks is also accomplished in ahydraulic press, and the method of this invention is applicable to thisoperation.

The actual pressing of the colloided powder into the desired sizestrands just prior to granulation is also accomplished by hydraulicpresses. The presses may be of varying diameter but comparatively smallpresses, say four inches in diameter, are used for double base powderwhile large presses, say up to twenty inches in diameter, may be usedfor single base powders. The operation of these presses is made safer bycontrolling the gaseous medium therein so that an atmosphere incapableof supporting combustion is maintained.

It will be understood that the present inven tion may be used in any ofthe various hydraulic pressing operations necessary in the production ofsmokeless powder. Further, that the invention is applicable withoutspecial regard for the actual composition of the powder being pressed.The invention provides for means whereby the production of any of thenumerous formulations of both single and double base powders may beaccomplished in a safer manner.

In ignition, combustion, and/or explosion of the solvent vapors withinthe hydraulic presses is believed to be due in the main to the increasein the temperature of the gas phase occurring upon compression, but maybe aggravated by friction or conditions which are undeterminable. Therate of compression, of course, controls the temperature rise but thisrate is diflicult if not impossible to control in operations due tovariations in charges, weights, and vapor concentration. However,compression ratio must be considered and allowances made for most severeconditions. If the powder itself is ignited from any cause, the inertatmosphere will not snufi out the flame but ignition of the powder priorto ignition of the vapors is believed to be a rare occurrence.

To show that ignition may be reduced or eliminated by the method of thisinvention, Table I in which the effect on ignitability produced by theaddition of two inert gases, nitrogen and carbon dioxide, to analcohol-acetone vapor is presented below. The compression ratio in theseexperiments were closely controlled.

asvareo Tsar: I

Suppression of compression ignition of acetonealcohol vapor-air mixturesby inert gases Combustible vapor Inert gas, volume,

Type of vapor Ignitabllity No ignition. Ignition. No ignition. Ignition.No ignition. Ignition. No ignition. Ignition. No ignition. Ignition. Noignition.

Acetone-alcohol I 25.591 001.: lat 66;:

1 Liquid of the composition 62.5 anhydrous acetone and 37.5% ethylalcohol (as volume was used to saturate air at about 35 C.

It was calculated from vapor pressure data that the vapor composi tionin e uilibrium with this liquid contained about 30% acetone, 6% alcohoand 1% water vapor (by volume). Thus the combustible vapor concentrationwas about 36%, and the above mixtures were obtained by diluting theconcentrated vapor with the proper amounts 0! air or inert gas. Similareffects of inert gas were noted at other ratios of acetone to alcohol.

1 The underlined values show the minimum compression ratios at which itwas possible to get ignition oi the vapor mixtures. The maximumcompression ratios at which non-ignition invariably was observed arealso recorded. in case of the mixture containing 48.5% carbon dioxide,no ignition occurred at the maximum compression ratio convenient toapply in the apparatus used.

The apparatus used to study the compression ignition of solventvapor-air mixtures given in Table I consists of a cylinder about twoinches in diameter with a tight-fitting piston with a ten-inch stroke.The gas-vapor mixtures of a predetermined composition were introduced atnormal temperatures into the cylinder at atmospheric pressure and thepiston rapidly thrust into the cylinder to a predetermined compressionratio. The speed of the piston motion was such that adiabatic conditionsprevailed. The superheating of the gas-vapor mixtures brought abouttheir explosion without any ignition device. By regulation of thecompression ratios obtained, it was possible to determine a maximumcompression ratio for which no ignition would occur and a minimumcompression ratio for which ignition was certain to take place. Thesevalues are recorded in Table I above. By insertion of solvent wetsmokeless powder in the bottom of the cylinder, it was found thatadiabatic compression ignition of the solvent vapor-gas mixture wasinvariably followed by ignition and burning of the smokeless powder,whereas, when the conditions of the adiabatic compression heating of thegas phase were insufficient to cause its ignition, no ignition of thepowder itself would occur.

The preferable method for controlling the composition of the gaseousmedium in the hydraulic presses is by an injection valve enteringthrough the ram or side of press, but many other methods are applicablefor this control and such means as inserting solid carbondioxidedirectly into the press, allowing a current of inert gas to continuallysweep out the press either by entering the top or bottom openings,suitable valves within the operating mechanism, or by maintaining theentire press in an inert atmosphere are contemplated.

The advantages of the process of this invention is in the safety ofoperation, in the increased eiiiciency brought about by the lack ofshutdown for repairs and in the increased production possible byincreasing ram speeds. The elimination of -pressing whereby ignitionwithin said press is avoided.

2. In the manufacture of propellant powder of the single base type bymixing, pressing and granulating, the step which comprises maintainingan inert atmosphere in contact with the powder during the pressingoperation whereby ignition of solvent vapors is prevented.

3. In the manufacture of propellant smokeless powders from admixturescomprising nitrocellulose and volatile solvents which includes mixing,pressing and granulating, the step of contacting said powder during saidpressing with a gaseous medium containing sufiicient nitrogen to rendersaid medium incapable of supporting combustion whereby ignition of saidsolvent and said powder is prevented.

4. In the manufacture of propellant smokeless powders from admixturescomprising nitrocellulose and volatile solvents which includes mixing,pressing and granulating, the step of contacting said powder during saidpressing with a gaseous medium containing suflicient carbon dioxide torender said medium incapable of supporting combustion whereby ignitionof said solvent and said powder is prevented.

5. In the manufacture of propellant smokeless powders from admixturescomprising nitrocellulose and volatile solvents which includes mixing,pressing and granulating, the step of contacting said powder during saidpressing with a gaseous medium containing sufiicient exhaust gas torender said medium incapable of supporting combustion whereby ignitionof said solvent and said powder is prevented.

6. In the manufacture of propellant powder from admixtures comprisingnitrocellulose, liquid explosive nitric esters and volatile solvents,the

step of reducing the oxygen concentration of the gaseous medium incontact therewith to produce a gaseous medium characterized bynon-ignitability, and pressing said powder in said reduced oxygenconcentration through forming dies.

'7. In the manufacture of propellant powder of the double base type bymixing, pressing and granulating, the step which comprises maintainingan inert atmosphere in contact with the powder during the pressingoperation whereb ignition of solvent vapors is prevented.

8. The method of operating a smokeless powder extrusion press comprisingloading the chamber of the press with a colloided admixture whichcomprises nitrocellulose and volatile solvents, lowering the ram intothe chamber of the press, introducing a current of inert gas into saidchamber whereby the oxygen concentration of said chamber is reducedbelow the ignition point and then lowering the ram onto the admixtureand extruding the admixture by application of pressure.

9. In the manufacture of propellant powder of the double base type bymixing, pressing, and granulating, the steps which comprise maintainingan inert atmosphere in contact with the powder during the mixingoperation and during the pressing operation whereby ignition of solventvapors is prevented. I

10. In the manufacture of propellant powder of the single base type bymixing, pressing, and granulating, the steps which comprise maintainingan inert atmosphere in contact with the powder during the mixingoperation and during the pressing operation whereby ignition of solventvapors is prevented. 11. In the manufacture of propellant powder of thedouble base type by mixing, pressing, and granulating, the steps whichcomprise maintaining a carbon dioxide atmosphere in contact with thepowder during the mixing operation and during the pressing operationwhereby ignitionof solvent vapors is prevented.

12. In the manufacture of propellant powder of the single base type bymixing, pressing, and granulating, the steps which comprise maintaininga carbon dioxide atmosphere in contact with the powder during the mixingoperation and during the pressing operation whereby ignition of solventvapors is prevented.

LEON W. BABCOCK.

